Main distribution frame-mounted central office subscriber carrier channel unit shelf

ABSTRACT

This shelf is set inside a main distribution frame (MDF) between horizontal crossbars thereof. The shelf is supported by a pair of flanges that project from the top thereof and rest on adjacent horizontal crossbars. The flanges are offset from each other so that identical shelves can be mounted side-by-side in adjacent openings between crossbars of the MDF. The top of the shelf is shaped to form a neck section that hangs over the horizontal mounting bar on the front of the MDF for supporting the shelf and a vertical faceplate. Several compartments are formed inside the shelf by longitudinal ribs. Pairs of vertically aligned opensided and closed-sided retainer sockets in each compartment are attached to the top and bottom inside walls of the shelf at the back thereof. Each pair of sockets receives mounting tabs on a printed-circuit card connector that is held in place by a flexible retainer arm which snaps into a locking position when the connector tabs are forced into the sockets. A major portion of the bottom of the shelf is open at the front thereof for loading individual subscriber carrier channel units into the compartments. Each channel unit includes openings in the back and top front thereof and a printed circuit card that plugs into an associated connector at the back of the shelf. Openings in the back of the shelf and the bottom and top thereof near the neck section form a chimney that draws air through and cools the channel units. Grooves are provided adjacent the openings in the top wall of each compartment for snap-locking the channel units into the shelf. Wires from the connectors are ducted through cable troughs on the side of the shelf to the front thereof. In a preferred embodiment of the invention, a line terminal block is connected to the faceplate so that it is aligned with a horizontal mounting bar when the shelf is set in an MDF.

United States Patent I [1 1 Stumpf et al.

1 Apr. 2, 1974 MAIN DISTRIBUTION FRAME-MOUNTED CENTRAL OFFICE SUBSCRIBER CARRIER CHANNEL UNIT SHELF [75] Inventors: Gene L. Sturnpf, Belmont; Donald G. Tweed, Mountain View, both of Calif.

[73] Assignee: GTE Lenkurt Incorporated, San

Carlos, Calif.

22 Filed: Oct. 4, 1972 21 Appl. No.: 295,055

[52] US. Cl 317/99, 339/176 MP, 312/3, 317/101 CB, 317/101 R [51] Int. Cl. H02b 1/04 [58] Field of Search 317/100, 101 CB, 101 DH, 317/118, 120, 122, 101 R, 117, 99; 339/17 N, 119 R, 125 R, 126 R, 198 S, 176 MP;

Primary Examiner-Herman J. Hohauser Assistant ExaminerGerald P. Tolin Attorney, Agent, or Firm-Leonard R. Cool; Russell A. Cannon; T. C. Jay

[57] ABSTRACT This shelf is set inside a main distribution frame (MDF) between horizontal crossbars thereof. The shelf is supported by a pair of flanges that project from the top thereof and rest on adjacent horizontal crossbars. The flanges are offset from each other so that identical shelves can be mounted side-by-side in adjacent openings between crossbars of the MDF. The top of the shelf is shaped to form a neck section that hangs over the horizontal mounting bar on the front of the MDF for supporting the shelf and a vertical faceplate. Several compartments are formed inside the shelf by longitudinal ribs. Pairs of vertically aligned open-sided and closed-sided retainer sockets in each compartment are attached to the top and bottom inside walls of the shelf at the back thereof. Each pair of sockets receives mounting tabs on a printed-circuit card connector that is held in place by a flexible retainer arm which snaps into a locking position when the connector tabs are forced into the sockets. A major portion of the bottom of the shelf is open at the front thereof for loading'individual subscriber carrier channel units into the compartments. Each channel unit includes openings in the back and top front thereof and a printed circuit card that plugs into an associated connector at the back of the shelf. Openings in the back of the shelf and the bottom and top thereof near the neck section form a chimney that draws air through and cools the channel units. Grooves are provided adjacent the openings in the top wall of each compartment for snap-locking the channel units into the shelf. Wires from the connectors are ducted through cable troughs on the side of the shelf to the front thereof. In a preferred embodiment of the invention, a line terminal block is connected to the faceplate so that it is aligned with a horizontal mounting bar when the shelf is set in an MDF.

29 Claims, 19 Drawing Figures PAIENTEDAPR 21914 3 801 8 73 sum 3 0F 6 FIG. 3

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MAIN DISTRIBUTION FRAME-MOUNTED CENTRAL OFFICE SUBSCRIBER CARRIER CHANNEL UNIT SHELF BACKGROUND OF THE INVENTION This invention relates to carrier telephone systems, and more particularly to a shelf for mounting a subscriber carrier channel unit terminal in a main distribution frame (MDF) of a telephone central office.

Subscriber carrier equipment is used in combination with existing physical line telephone equipment to provide additional subscriber telephone circuits without increasing the number of physical cable pairs in the outside plant. In a conventional subscriber carrier telephone system, the central office subscriber carrier equipment includes shelves of individual plug-in channel units that are stacked in racks which are physically spaced apart from the MDFs through which subscriber-physical cable pairs are connected to other central office equipment such as incoming relays and line finders. These racks of central office subscriber carrier equipment must be wired to line terminal blocks (LTDs) on MDFs. Since this is a major modification of existing telephone equipment, telephone engineers are normally required to supervise the specification, ordering, and installation of such equipment. This increases the time and cost to install additional equipment and is burdensome and inconvenient when only a small increase in the number of subscriber circuits is desired.

If there is an immediate need for a small number of additional subscriber telephone circuits, the aforementioned. technique for increasing subscriber capacity may be impractical. The requirement could be for a permanent installation to provide an existing customer such as a business with. a second phone, or for temporary installations to provide seasonal services in vacation areas. Single-channel, station carrier equipment that adds only a single carrier channel to an existing physical pair of lines may satisfy this need. It is desirable that the central office terminal for such an installation be conveniently located with respect to the MDF to which it must be wired and yet not interfere with the future installation of wires or block the aisles formed by the rows of MDFs. An MDF (a portion of which is illustrated in FIG. 1) consists of a plurality of vertical and horizontal mounting. bars 24. and 25 27, respectively, which are normally spaced 8 inches apart. LTBs 36 connected to the front of the horizontal mounting bars provide for connection of an incoming physical cable pair 28a, 29a to relays and line finders (not shown) through jumper wires 37, 38 and lines 34, 35. In a prior-art system, a channel unit is mounted on a horizontal or vertical mounting bar of an MDF by removing a channel unit printed-circuit card from the cover, attaching a mounting bracket to the cover, securing the bracket on the cover to an MDF mounting bar, inserting the printed-circuit card into the shelf, and then connecting wires or cables to a connector on the channel unit that is considerably different from the LTB normally employed-on an MDF. This means that it will take an installer longer to make electrical connection for this channel unit than for a physical cable pair. Also, this channel unit fills much of the vertical space between adjacent horizontal front: mounting bars and interferes with installing additional wiring-therebetween. If a number of individual channel units are added to the system, a similar procedure is employed to securethe individual channel unit covers together before one of them is attached to an MDF mounting bar. An alternate prior approach is to temporarily hang a housing, which includes several individual channel units, on a horizontal MDF mounting bar until a rack of channel units is justified and installed near the MDF. This mounting technique is inconvenient since such a housing hung on a horizontal mounting bar sticks out in front of the MDF and partially blocks the main aisle and interferes with the installation of additional wiring between adjacent horizontal mounting bars. Even if the temporary housing is hung on a crossbar at the end of an MDF, it will block the aisle there. This housing also employs a different type of connector than the LTB normally used on an MDF.

An object of this invention is the provision of an improved shelf for mounting subscriber carrier channel units in an MDF.

Another object is the provision of an improved MDF mounted subscriber carrier channel unit shelf that drops into place inside an MDF between horizontal crossbars on which it rests with a front lip hanging over the associated horizontal mounting bar and supporting an LTB thereon.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a portion of an MDF in a central office with an MDF subscriber carrier channel unit shelf embodying this invention mounted therein;

FIG. 2 is a front perspective view of an MDF channel unit shelf embodying this invention with an LTB and faceplate mounted on the front of the shelf, and being taken from one side and the top of the shelf;

FIG. 3 is a front perspective view of the MDF channel unit shelf in FIG. 2, with the LTB and faceplate removed therefrom and with a channel unit and a printed circuit card connector mounted therein, and being taken from the other side and bottom thereof;

FIG. 4 is a top view of the MDF shelf in FIG. 3;

FIG. 5 is a left side elevation view of the MDF shelf in FIG.- 3; 7

FIG. 6 is a section view of the MDF shelf taken along the lines 66 in FIG. 4;

FIG. 7 is a front elevation view of the faceplate;

FIG. 8 is a top view of the faceplate in FIG. 7;

FIG. 9 is a section view of the faceplate taken along lines 9-9 in FIG. 7;

FIG. 10 is a right-side elevation view of the printedcircuit card connector as it is viewed in FIG. 3;

FIG. 1 l is a front elevation view of the printed-circuit card connector as it is viewed in FIG. 3;

FIG. 12 is a section view of the MDF shelf taken along the lines l212 in FIGS. 4 and 6;

FIG. 13' is a section view of a portion of the MDF shelf taken along the lines 13-13 in FIG. 12;

FIG. 14 is a left-side elevation view of a channel unit;

FIG. 15 is a rear elevation view of a channel unit;

FIG. 16 is an enlarged section view taken along lines l6l6 in FIG. 14 and showing the shape of the snap lock holding fixture on the channel unit cover;

FIG. 17 is an enlargedsection view of a groove in and bead on the top walls of a shelf and taken along lines 1717' in FIG. 4;

FIG. 18 is the enlarged section view in FIG. 17 with the snap lock on the channel unit cover attached thereto; and

FIG. 19 is an enlarged section view taken along lines 66 in FIGS. 4 and 12, with part of the shelf cut away.

DESCRIPTION OF THE REFERRED EMBODIMENTS A distribution frame in a telephone central office is essentially the dividing point between the outside plant and local inside plant of a telephone system. It provides the means for connecting incoming subscriber physical cable pairs to line finders and other associated switching equipment in the central office. More specifically, it provides an interconnection stage in which protective devices can be connected in series with or between incoming subscriber physical cablepairs and central office equipment; to which the physical cable pairs can be connected and arranged to be easily identified; to which central office switching equipment can be connected through connector cables; and in which associated switching equipment cabling and subscriber physical cable pairs can be electrically connected together by jumper wires.

Referring now to the perspective view of a portion of the horizontal side of a distribution frame in FIG. 1, an

MDF generally comprises vertical braces 3 6 having jumper rings 7 connected thereto; a plurality of horizontal braces 8 and 9 connected to the vertical braces; a plurality of horizontal crossbars 11 secured to associated vertical braces; a plurality of vertical mounting bars such as bar 24 on one side of the MDF (the side receding into the plane of the paper) and connected to the one ends of associated horizontal crossbars; and a plurality of horizontal mounting bars 25 27 on the other side of the MDF and connected to the other ends of associated horizontal crossbars l1 20. The horizontal and vertical spacing between adjacent crossbars 11 20 are both 8 inches on a standard MDF. An incoming physical subscriber cable pair 28a, 29a is connected to associated protectors of terminal block 30 on vertical mounting bar 24. A connector cable 33 from central office switching equipment (not shown) is laid on crossbars l1 12 in the vertical opening be tween the latter and the adjacent crossbar 15. A pair of wires 34, 35 from cable 33 is connected to the lower pins of two terminals on the LTB 36 that is attached to mounting bar 25. Jumper wires 37 and 38 are attached to associated pins of terminal block 30, are threaded through jumper ring 7' and the opening between crossbars 12 and I5, and are attached to the upper pins of the same two terminals on LTB 36 in order to interconnect a first subscriber physical cable pair 28a, 29a to wires 34, 35 and thus to associated switching equipment. It is desirable to keep as much as-possible 'of the vertical opening between horizontal crossbars free of equipment so that installers can easily thread connector cables 3 and jumper wires 37, 38 therethrough as they are needed.

A channel unit shelf 41 embodying this invention fits inside an MDF as shown in FIG. 1. The shelf 41, which is shown in detail in FIG. 2, drops into the opening between horizontally spaced apart crossbars l5 and 16 of the MDF. Flanges 42 and 43 protrude from the top 44 of the shelf to support the latter on the crossbars I5 and 16. The front 45 of the shelf hangs over, and rests on, horizontal mounting bar 26. If a particular MDF does not include a front horizontal mounting bar 26, it can be easily added to support the shelf. Shelf 41 is preferably secured to mounting bar 26 by screws since the horizontal mounting bar already contains threaded holes for attaching LTBs thereto. The inside of the shelf is divided into five compartments by four longitudinal ribs 47 50 and the side walls 51 and 52, see FIGS. 3 and 4. The major portion of the bottom of the shelf is open as is shown in FIG. 3 for loading individual channel units such as unit 53 into a compartment of the shelf as is described more fully hereinafter.

In a preferred embodiment of this invention, an LTB 55 that is similar to the LTB 36 that is normally attached to the horizontal mounting bars 25 27 is attached to the faceplate 56 of the shelf. This enables a telephone equipment installer to work with familiar components when connecting each of the jumper wires 37 and 38' and connector wires 31 and 32, and connector wires 39 and 40 to different terminals pins on LTB 55 for connecting a central office channel unit 53 in shelf 41 to a second physical subscriberpair 26b, 29b and the switching equipment. It is only necessary to wire the shelf 41 for electrical power and alarm signaling to complete installation of a subscriber carrier unit in the shelf. Printed-circuit card connectors 57 (see FIGS. 10 and 11) are mounted in the rear of each compartment (see FIG. 3). The shelf is prewired with wires (not shown) from the back of connectors 57 which run through the slot 58 in wall 51, cable troughs 59 61, and the slotted openings in fingers 62 66 (see FIG. 2) to terminals of LTB 55 on the front thereof. Thus, when an individual channel unit 53 in FIGS. 14 16 is loaded into the shelf with the end 67 of the channel unit printed-circuit card 68 in a connector 57, channel unit 53 is automatically wired to terminals on LTB 55.

The shelf 41 is dimensioned so as to only fill about half of the vertical space between horizontal mounting bars 25 and 26. This leaves sufficient room to place jumper wires and cabling in this area, preferably near the back of the shelf. Individual channel units 53 are inserted into the shelf from the front and bottom thereof as is seen in FIG. 3. The channel units may be inserted into the shelf either before or after the latter is set into the MDF. Openings or slots 72 in the top of the shelf (see FIGS. 2 4) allow for circulation of air through the rear slots 117 (see FIGS. 12 l3) and up through the front of the shelf, over channel units53 and out openings 72 to cool electrical components in the units 53.

Referring now to the FIGS. 2 6, the flanges 42 and 43 protrude from the top 44 over the associated side walls 51 and 52. Ribs 73 are formed on flanges 42 and 43 for providing reinforcement thereof. The flanges are offset from each other so that physically identical shelves 4lcan be set side-by-side in adjacent openings between crossbars 'such as 15, 16 and 16, 17 of the MDF.

The side walls 51 and 52 are dimensioned to form a neck section 74 adjacent the front plate 75 (see FIG. 5) The shoulder 76 in the neck section 74 rests on the horizontal mounting bar 26 of the MDF. Screws are inserted in the holes 77a and 77b (see FIG. 3) in front plate 75 and are screwed into threaded holes on the horizontal mounting bar 26 to secure the shelf to the latter. Ribs 78 83 on front plate 75 extend over the top of shoulder 76 and into the trough section 84 where they are joined to one side of crossbar 85 for reinforcing the neck section 74 of the shelf (see FIG. 4). A second plurality of reinforcing ribs 87 90 extend between the other side of crossbar 85 and associated fingers 92 95 that are formed in the top 44 and define the air hole openings 72. A flange 99 which protrudes at an angle downwardly from the front plate 75 is joined to the other ends of ribs 78 83 and to the side flanges 100 and 101 on the front plate (see FIG. 5).

Bosses 102 and 103 having apertures therethrough are formed on front plate 75 over recesses in which nuts can be inserted. These bosses provide flat surfaces for mating with corresponding bosses 104 and 105 on faceplate 56 (see FIGS. 7 9) and the holes therein provide a convenient mechanism for attaching faceplate 56 and the dielectric bars 107 109 and terminal posts or pins 110 forming the LTB 55 (see FIG. 2) to the shelf. Sockets 111 and 112 are formed in faceplate 56 for holding an alarm lamp and a fuse, respectively, (not shown). A plurality of protrusions or fingers 62 66 having slots 62a 66a of gradually increasing length in the ends thereof protrude from the back of faceplate 56. The fingers 62 m 66 are located adjacent corresponding ribs 79 83 when faceplate 56 is attached to shelf 41. A plurality of apertures 115, 115' formed in faceplate 56 provide passageways for rapid threading of wires that are connected to terminal posts 110. Wires threaded through the lower apertures 115' are deflected by the tilted flange 99 up into the area of the trough 84. The openings 62a 66a in the fingers 62 66 provide an effective and convenient mechanism for holding wires from the LTB that extend across the trough 84.

The inside of shelf 41 is divided into 5 compartments that are each dimensioned to receive an individual channel unit 53 therein (see FIGS. 3 and 4). The bottom 46 of the shelf extends over approximately one quarter of the length of the shelf near the back thereof. This leaves a large opening in the bottom through which individual channel units 53 are loaded into the shelf. A rear wall 116 extends between the top 44 and bottom 46 near the center of the latter (see FIGS. 4 5). The portion of the bottom 46 in front of wall 116 isprimarily used as a short contact surface to support the channel units 53 rather than as a surface which holds the channel units. A rectangular opening 117 is formed in wall 1 16 at therear of each compartment for receiving the pinned end 128 of an'associated connector 57. Fins 118 extend towards the back of the shelf from the sections of wall 116 between the rectangular opening 1 17. The'fins 118 electrically isolate electrical connections to pins 127 of the connectors and provide reinforcement of the back of the shelf. The slots 118a that are formed in the ends of fins 118 adjacent the top 44 of the shelf provide passageways for wires as is described more fully hereinafter. The other slots ll8b in fins 118 are also used to pre-wire the shelf.

Longitudinal ribs 47 50 and 121 124 are formed on the inner surfaces of the top 44 and bottom 46, re spectively, of the shelf. Pairs of associated ribs, such as ribs 47, 121 and 48, 122, etc., are vertically aligned and in parallel planes that define the compartments in the shelf (see FIG. 12). The ribs 121 124 extend over the length of the bottom 46 in front of wall 116 (see FIGS. 4 6). These ribs 121 124 are relatively shallow since they serve primarily as an index or guide for the channel unit covers 53. The ribs 47 50 depend from the finger sections 92 and extend from the underside of trough 84 to a point above the bottom wall 46 and adjacent the rear wall 116 (see FIG. 6). The height of the ribs 47 50 is preferably much less than that of the shelf, although they may extend from the top 44 to the bottom 46 over the latter. Each of the fingers 91 96 has an elongated dimple or groove 119 and an elongated bead on each side of the front thereof which is adjacent the junction with an associated reinforcing rib section 87 90 or wall 51 52 (see FIGS. 4 and 17).

The connector 57 that is mounted at the rear of each compartment is shown in detail in FIGS. 10 and 11. The connector 58 may be a molded plastic part having sockets 126 in one side thereof that are connected to corresponding prongs or terminal pins 127 on the other side thereof. The body section 128 of the connector is dimensioned to fit into the openings 117 in the rear wall 116. Tabs 129 and 130 are formed on the top and bottom of the connector for aligning and mounting the connector in the shelf as is described more fully hereinafter.

Referring now to FIGS. 12, 13, and 19, a pair of sockets 132 and 133 are formed in each compartment on the inner surfaces of top 44 and bottom 46, respectively, and next to the rear wall 116. Sockets 132 and 133 are vertically aligned across openings 117 in the rear wall 116 and are located adjacent the vertical planes through associated ribs 47 50 and 121 124 and wall 51 (see FIG. 12). The sockets 132 and 133 have openings in the surfaces thereof that are facing each other for receiving the tabs 129 and 130, respectively, of connector 57. The bottom socket 133 is closed on all sides whereas the side of the upper socket 132 facing away from the adjacent plane through ribs 49 and 123, for example, is open (see FIGS. 6, 12, 13, and 19). A pair of horizontal bars 134 and 135 are formed. on the inside surface of wall 116 below and above the sockets 132 and 133, respectively.

An arm 136 is also formed on the rear wall 116 in each compartment. Each arm 136 protrudes from wall 116 into the compartment area and curves over the opening 117 in the latter toward an imaginary vertical line through sockets 132 and 133. Although laterally spaced from the sprockets 132 and 133, the arm 136 is located proximate the sockets. The arms 136 are preferably made of a resilient material so that they can be bent toward wall 116 and out of alignment with the openings in sockets 132 and 133. The connector 57 is mounted in the shelf by inserting tab 130 in socket 133, pressing the connector against arm 136 to move the latter out of alignment with the opening in socket 132, and pushing the connector sideways until tab 129 rests in the opening in socket 132. The arm 136 then snaps back to its normal position and the free end thereof holds the connector in place at the back of the shelf and adjacent wall 116.

The channel unit 53 comprises a molded plastic cover 139 having a plurality of posts 140 protruding from the inner. side wall thereof and through holes in printed-circuit (PC) card 68. The PC card is secured in cover 139 by deforming the ends of the posts 140 over the card, e.g., with the heat of a soldering iron or by ultrasonic welding (see FIGS. 14 and Electrical circuits formed on the card are connected to other circuits by pins on the end 67 thereof. An opening 141 is formed in the end wall 142 of the cover. The front of the cover is tapered to form a lower section 143 having a handle 144 formed thereon and an upper section 145 having an opening 146 with a grill 147 therein. The openings 141 and 146 in the cover allow for circulation of air through, and the removal of heat from, he cover. A step 148 is formed in the bottom 149 of the cover. A holding fixture 152 is formed on the top of cover 139 and comprises a downwardly depending, elongated bead 153 connected by a flexible shank 154 to a flange 156 and thus to the cover (see FIGS. 14 18). Channel unit 53 is loaded into the shelf 41 from the bottom of the latter by resting the surface 148 of cover 139 on the bottom 46 of the shelf, and simultaneously inserting the end 67 of card 68 into the openings 126 in connector 57 and forcing the bead 153 over corresponding beads 120 of a pair of fingers 91 96. Thus, it is seen that a channel unit 53 is supported in the shelf by both the 'bottom 46 and the holding fixture 152. The bars 132 and 133 provide a stop that the connector presses against when the cover is inserted into the shelf.

The manufacture of shelf 41 is facilitated by forming it in two parts from a plastic material such as LEXAN by injection molding. One part comprises the bottom 46, wall 116, fins 118, ribs 121 124, sockets 132 and 133, stops bars 134 and 135, and the arm 136. The other part comprises the top 44, side walls 51 and 52, and ribs 47 50. A continuous bar 157 and segmented bar 158 are formed on the inside surface of top 44 (see FIGS. 4 6, l2, and 19). The shelf is assembled by inserting the top of wall 116 between bars 157 and 158 and the bottom 46 in the notched opening in walls 51 and 52 (see FIG. 19). The parts of the shelf are joined together by ultrasonic welding. Alternatively, the parts can be bonded together with a suitable epoxic cement.

Although this invention is described in relation to a preferred embodiment thereof, modifications will be apparent to those skilled in the art. By way of example, one side of both sockets 132 and 133 may be open, and there can be two arms 136 located adjacent opposite ends of the connector 57. Alternatively, the front wall of one or both of the sockets 132 and 133 may be open and arms 136 located to contact the front of connector 57. Also, the tabs 129 and 130 may be omitted and the opposite endsof connector 57 inserted in the openings in sockets l32and 133. This invention is therefore defined by the following claims rather than the above detailed description.

What is claimed is:

1. A shelf for receiving a plurality of individual plugin central office subscriber carrier channel unit covers and for mounting inside a telephone central office main distribution frame (MDF) between adjacent horizontal crossbars thereof, said shelf comprising a top wall,

a pair of opposing side walls,

a rear wall proximate one end of said top wall and the shelf at the back of the latter, I

a bottom wall opposing said top wall proximate the one end of the latter,

means for connecting said walls together so as to form a rigid receptacle,

a front section connected to the other end of said top wall, said front section comprising an upright front plate, and

a shoulder forming an open neck between said front plate and said side and top walls, said shoulder being dimensioned for supporting the shelf in an MDF with the front plate in front of, and the shoulder resting on, a horizontal mounting bar on the front of an MDF, and

first and second flanges projecting beyond associated side walls for resting on adjacent horizontal crossbars of an MDF to support the shelf when it is mounted in an MDF.

2. The shelf according to claim 1 including means for compartmentalizing the inside of the shelf, each of'the compartments dimensioned for receiving an individual pluggable channel unit cover.

3. The shelf according to claim 2 wherein said bottom wall extends 'over only a small portion of the bottom of the shelf proximate the back of the latter, the bottom of the shelf being open over the majorportion of its lenght at the front thereof for pluggably inserting individual channel unit covers into the shelf from the bottom-front of the latter.

4. The shelf according to claim 3 wherein a slot is cut in the top wall in each compartment at the front of the shelf.

5. The shelf according to claim 4 wherein a slot is formed in said rear wall in each compartment, the openings in said bottom and top walls forming a chimney through which warm air produced in the shelf in channel units is forced out the top slots by cooler air drawn in at the bottom opening and rear slots.

6. The shelf according to claim 5 including means in each of the compartments for receiving opposing ends of an elongated electrical printed circuit connector and snap-locking the connector in the compartment.

7. The shelf according to claim 6 wherein said lastnamed receiving means comprises first and second sockets each having an open end, one wall of one of said sockets being open, said sockets being securely mounted in the compartment proximate the back of the shelf with the open ends of saidsockets facing each other for receiving opposite ends of a connector.

8. The shelf according to claim 7 including a flexible member rigidly secured in the shelf and being bent away from its normal position when ends for a connector are forced into open ends of associated sockets, said flexible member snapping back to its normal position to hold the connector ends in said associated sockets.

9. The shelf according. to claim 8 wherein the one wall is a side wall of one of said sockets.

10. The shelf according to claim 8 wherein the one wall is a front wall of oneof said sockets.

11. The shelf according to claim 6 wherein said lastnamed receiving means comprises a first socket having closed sides and an open end and a second socket having one open side and an open end securely mounted in the compartment proximate the back of the shelf with the open ends of the sockets facing each other for receiving opposite ends of a connector.

12. The shelf according to claim 11 including a flexible member rigidly secured in the shelf and being bent away from its normal position when ends of a connector ends are forced into open ends of associated sockets, said flexible member snapping back to it normal position to hold the connector ends in said associated sockets.

13. The shelf according to claim 3 wherein the width of each of said flanges is a small fraction of the length of the shelf, said flanges being offset from each other for seating identical shelves in an MDF in adjacent openings between horizontal crossbars.

14. The shelf according to claim 3 including a line terminal block and means for attaching said block to said front plate.

15. The shelf according to claim 5 including an upright faceplate having a plurality of apertures therethrough and being secured to said front plate with spaces therebetween, said front plate having a tilted flange in back of at least some of the apertures for enabling threading of wires between said plates and through the some apertures.

16. The shelf according to claim including a plurality of troughs on the outside surface of one of said side walls for holding wires extending from the back to the front of the shelf.

17. The shelf according to claim 16 wherein said faceplate includes a plurality of fingers on the back thereof extending over said front section, said fingers having openings in the ends thereof towards the back of the shelf for holding wires that are threaded through the some apertures.

18. The shelf according to claim 5 wherein said compartmentalizing means comprises a plurality of top ribs depending from the inside surface of said top wall and bottom ribs projecting from the inside surface of said bottom wall, each top rib being axially aligned with an associated bottom rib.

19. The shelf according to claim S wlherein at least a portion of one of said top and bottom walls is integrally molded as a single part with said rear wall.

20. The shelf according to claim 19 including first and second spaced apart guide bars extending traversely in the shelf on the inside surface of the other of said top and bottom walls and receiving said rear wall therebetween for aligning the latter in the shelf.

21. The shelf according to claim 12 wherein said rear wall is spaced away from the one end of the shelf, and including upright ribs separating adjacent connectors for providing electrical isolation of wires connected thereto.

' 22. The shelf according to claim 21 wherein the tops of said upright ribs are spaced from said top wall for threading wires above said rear ribs. I

23. A shelf for receiving a plurality of individual plugin central office subscriber carrier channel unitcovers and being mounted'inside a telephone central office main distribution frame (MDFlbetween adjacent horizontal crossbars thereof, said shelf comprising a top wall j I a pair of opposing side walls,

a rear wall proximate one end of said top wall and the shelf at the back of the latter, a bottom wall opposing said top wall proximate the one end of the latter,

means for connecting said walls together so as to form a rigid receptacle,

a front section connected to the other end of said top wall, said front section comprising an upright front plate, and

a shoulder forming an open neck between said front plate and said side and top walls, said shoulder supporting the shelf in said MDF with the front plate in front of and the shoulder resting on a horizontal mounting bar on the front of said MDF, and

first and second flanges projecting beyond associated side walls of the shelf and resting on adjacent horizontal crossbars of, and supporting the shelf in said MDF.

24. The shelf according to claim 23 including means for compartmentalizing the inside of the shelf, each of the compartments being dimensioned for receiving an individual pluggable channel unit cover; and wherein said bottom wall extends over only a small portion of the bottom of the shelf proximate the back of the latter,

. the bottom of the shelf being open over the major portion of its length at the front thereof for pluggably inserting individual channel unit covers into the shelf from the bottom front of the latter.

25. The shelf according to claim 24 wherein a slot is formed in the top wall in each compartment at the front of the shelf; and wherein a slot is formed in said rear wall in each compartment, the openings in said bottom and top walls forming a chimney through which warm air produced in the shelf in channel units is forced out the top slots by cooler air drawn in at the bottom opening and rear slots.

26. The shelf according to claim 25 including a plurality of elongated electrical printed-circuit card connectors, and means in each of the compartments receiving opposing ends of one of said connectors and snap-locking said one connector in the compartment, said receiving means comprising first and second sock ets each having an open end, one wall of one of said sockets being open, said sockets being securely mounted in the compartment proximate the back of the shelf with the open ends of said sockets facing each other and receiving opposite ends of the one connector; and a flexible member rigidly secured in the shelf and being bent away from its normal position when said one connector ends are forced into open ends of associated sockets, said flexible member snapping back to its normal position to hold said orie connector ends in said associated sockets.

27. The shelf according to claim 24 wherein the width of each of said flanges is a small fraction of the length of the shelf, said flanges being offset from each other for seating identical shelves in said MDF in adjacent openings between horizontal crossbars.

28. The shelf according to claim 27 including an upright faceplate having a plurality of fingers on the back thereof extending over said front section, having a plurality of apertures therethrough, and being secured to said front plate with spaces therebetween; said front plate having a tilted flange in back of at least some of the apertures for enabling threading of wires between said plates and through the some apertures; said fingers having openings in the ends thereof towards the back of the shelf for holding wires that are threaded through the some apertures.

29..The shelf accordingto claim 28 including a line terminal block attached to said faceplate. 

1. A shelf for receiving a plurality of individual plug-in central office subscriber carrier channel unit covers and for mounting inside a telephone central office main distribution frame (MDF) between adjacent horizontal crossbars thereof, said shelf comprising a top wall, a pair of opposing side walls, a rear wall proximate one end of said top wall and the shelf at the back of the latter, a bottom wall opposing said top wall proximate the one end of the latter, means for connecting said walls together so as to form a rigid receptacle, a front section connected to the other end of said top wall, said front section comprising an upright front plate, and a shoulder forming an open neck between said front plate and said side and top walls, said shoulder being dimensioned for supporting the shelf in an MDF with the front plate in front of, and the shoulder resting on, a horizontal mounting bar on the front of an MDF, and first and second flanges projecting beyond associated side walls for resting on adjacent horizontal crossbars of an MDF to support the shelf when it is mounted in an MDF.
 2. The shelf according to claim 1 including means for compartmentalizing the inside of the shelf, each of the compartments dimensioned for receiving an individual pluggable channel unit cover.
 3. The shelf according to claim 2 wherein said bottom wall extends over only a small portion of the bottom of the shelf proximate the back of the latter, the bottom of the shelf being open over the major portion of its lenghT at the front thereof for pluggably inserting individual channel unit covers into the shelf from the bottom-front of the latter.
 4. The shelf according to claim 3 wherein a slot is cut in the top wall in each compartment at the front of the shelf.
 5. The shelf according to claim 4 wherein a slot is formed in said rear wall in each compartment, the openings in said bottom and top walls forming a chimney through which warm air produced in the shelf in channel units is forced out the top slots by cooler air drawn in at the bottom opening and rear slots.
 6. The shelf according to claim 5 including means in each of the compartments for receiving opposing ends of an elongated electrical printed circuit connector and snap-locking the connector in the compartment.
 7. The shelf according to claim 6 wherein said last-named receiving means comprises first and second sockets each having an open end, one wall of one of said sockets being open, said sockets being securely mounted in the compartment proximate the back of the shelf with the open ends of said sockets facing each other for receiving opposite ends of a connector.
 8. The shelf according to claim 7 including a flexible member rigidly secured in the shelf and being bent away from its normal position when ends for a connector are forced into open ends of associated sockets, said flexible member snapping back to its normal position to hold the connector ends in said associated sockets.
 9. The shelf according to claim 8 wherein the one wall is a side wall of one of said sockets.
 10. The shelf according to claim 8 wherein the one wall is a front wall of one of said sockets.
 11. The shelf according to claim 6 wherein said last-named receiving means comprises a first socket having closed sides and an open end and a second socket having one open side and an open end securely mounted in the compartment proximate the back of the shelf with the open ends of the sockets facing each other for receiving opposite ends of a connector.
 12. The shelf according to claim 11 including a flexible member rigidly secured in the shelf and being bent away from its normal position when ends of a connector ends are forced into open ends of associated sockets, said flexible member snapping back to it normal position to hold the connector ends in said associated sockets.
 13. The shelf according to claim 3 wherein the width of each of said flanges is a small fraction of the length of the shelf, said flanges being offset from each other for seating identical shelves in an MDF in adjacent openings between horizontal crossbars.
 14. The shelf according to claim 3 including a line terminal block and means for attaching said block to said front plate.
 15. The shelf according to claim 5 including an upright faceplate having a plurality of apertures therethrough and being secured to said front plate with spaces therebetween, said front plate having a tilted flange in back of at least some of the apertures for enabling threading of wires between said plates and through the some apertures.
 16. The shelf according to claim 15 including a plurality of troughs on the outside surface of one of said side walls for holding wires extending from the back to the front of the shelf.
 17. The shelf according to claim 16 wherein said faceplate includes a plurality of fingers on the back thereof extending over said front section, said fingers having openings in the ends thereof towards the back of the shelf for holding wires that are threaded through the some apertures.
 18. The shelf according to claim 5 wherein said compartmentalizing means comprises a plurality of top ribs depending from the inside surface of said top wall and bottom ribs projecting from the inside surface of said bottom wall, each top rib being axially aligned with an associated bottom rib.
 19. The shelf according to claim 5 wherein at least a portion of one of said top and bottom walls is integrally molded as a single part with said rear wall.
 20. The shelf aCcording to claim 19 including first and second spaced apart guide bars extending traversely in the shelf on the inside surface of the other of said top and bottom walls and receiving said rear wall therebetween for aligning the latter in the shelf.
 21. The shelf according to claim 12 wherein said rear wall is spaced away from the one end of the shelf, and including upright ribs separating adjacent connectors for providing electrical isolation of wires connected thereto.
 22. The shelf according to claim 21 wherein the tops of said upright ribs are spaced from said top wall for threading wires above said rear ribs.
 23. A shelf for receiving a plurality of individual plug-in central office subscriber carrier channel unit covers and being mounted inside a telephone central office main distribution frame (MDF) between adjacent horizontal crossbars thereof, said shelf comprising a top wall a pair of opposing side walls, a rear wall proximate one end of said top wall and the shelf at the back of the latter, a bottom wall opposing said top wall proximate the one end of the latter, means for connecting said walls together so as to form a rigid receptacle, a front section connected to the other end of said top wall, said front section comprising an upright front plate, and a shoulder forming an open neck between said front plate and said side and top walls, said shoulder supporting the shelf in said MDF with the front plate in front of and the shoulder resting on a horizontal mounting bar on the front of said MDF, and first and second flanges projecting beyond associated side walls of the shelf and resting on adjacent horizontal crossbars of, and supporting the shelf in said MDF.
 24. The shelf according to claim 23 including means for compartmentalizing the inside of the shelf, each of the compartments being dimensioned for receiving an individual pluggable channel unit cover; and wherein said bottom wall extends over only a small portion of the bottom of the shelf proximate the back of the latter, the bottom of the shelf being open over the major portion of its length at the front thereof for pluggably inserting individual channel unit covers into the shelf from the bottom front of the latter.
 25. The shelf according to claim 24 wherein a slot is formed in the top wall in each compartment at the front of the shelf; and wherein a slot is formed in said rear wall in each compartment, the openings in said bottom and top walls forming a chimney through which warm air produced in the shelf in channel units is forced out the top slots by cooler air drawn in at the bottom opening and rear slots.
 26. The shelf according to claim 25 including a plurality of elongated electrical printed-circuit card connectors, and means in each of the compartments receiving opposing ends of one of said connectors and snap-locking said one connector in the compartment, said receiving means comprising first and second sockets each having an open end, one wall of one of said sockets being open, said sockets being securely mounted in the compartment proximate the back of the shelf with the open ends of said sockets facing each other and receiving opposite ends of the one connector; and a flexible member rigidly secured in the shelf and being bent away from its normal position when said one connector ends are forced into open ends of associated sockets, said flexible member snapping back to its normal position to hold said one connector ends in said associated sockets.
 27. The shelf according to claim 24 wherein the width of each of said flanges is a small fraction of the length of the shelf, said flanges being offset from each other for seating identical shelves in said MDF in adjacent openings between horizontal crossbars.
 28. The shelf according to claim 27 including an upright faceplate having a plurality of fingers on the back thereof extending over said front section, having a plurality of apertures therethrough, and being secured To said front plate with spaces therebetween; said front plate having a tilted flange in back of at least some of the apertures for enabling threading of wires between said plates and through the some apertures; said fingers having openings in the ends thereof towards the back of the shelf for holding wires that are threaded through the some apertures.
 29. The shelf according to claim 28 including a line terminal block attached to said faceplate. 